Don't modify hash arguments.

lib/mongo/collection.rb

@@ -172,6 +172,7 @@ module Mongo
     #
     # @core find find-instance_method
     def find(selector={}, opts={})
+      opts   = opts.dup
       fields = opts.delete(:fields)
       fields = ["_id"] if fields && fields.empty?
       skip   = opts.delete(:skip) || skip || 0
@@ -437,8 +438,9 @@ module Mongo
     #
     # @core indexes create_index-instance_method
     def create_index(spec, opts={})
-      opts[:dropDups] = opts.delete(:drop_dups) if opts[:drop_dups]
+      opts[:dropDups] = opts[:drop_dups] if opts[:drop_dups]
       field_spec = parse_index_spec(spec)
+      opts = opts.dup
       name = opts.delete(:name) || generate_index_name(field_spec)
       name = name.to_s if name
 
@@ -466,7 +468,7 @@ module Mongo
       now = Time.now.utc.to_i
       field_spec = parse_index_spec(spec)
 
-      name = opts.delete(:name) || generate_index_name(field_spec)
+      name = opts[:name] || generate_index_name(field_spec)
       name = name.to_s if name
 
       if !@cache[name] || @cache[name] <= now
@@ -559,7 +561,7 @@ module Mongo
     def map_reduce(map, reduce, opts={})
       map    = BSON::Code.new(map) unless map.is_a?(BSON::Code)
       reduce = BSON::Code.new(reduce) unless reduce.is_a?(BSON::Code)
-      raw    = opts.delete(:raw)
+      raw    = opts[:raw]
 
       hash = BSON::OrderedHash.new
       hash['mapreduce'] = self.name

lib/mongo/gridfs/grid.rb

@@ -65,7 +65,7 @@ module Mongo
     #
     # @return [Mongo::ObjectId] the file's id.
     def put(data, opts={})
-      filename = opts.delete :filename
+      filename = opts[:filename]
       opts.merge!(default_grid_io_opts)
       file = GridIO.new(@files, @chunks, filename, 'w', opts=opts)
       file.write(data)

lib/mongo/gridfs/grid_file_system.rb

@@ -93,6 +93,7 @@ module Mongo
     #
     #  @return [Mongo::GridIO]
     def open(filename, mode, opts={})
+      opts = opts.dup
       opts.merge!(default_grid_io_opts(filename))
       del  = opts.delete(:delete_old) && mode == 'w'
       file = GridIO.new(@files, @chunks, filename, mode, opts)

lib/mongo/gridfs/grid_io.rb

@@ -55,6 +55,7 @@ module Mongo
       @chunks       = chunks
       @filename     = filename
       @mode         = mode
+      opts          = opts.dup
       @query        = opts.delete(:query) || {}
       @query_opts   = opts.delete(:query_opts) || {}
       @fs_name      = opts.delete(:fs_name) || Grid::DEFAULT_FS_NAME
@@ -410,6 +411,7 @@ module Mongo
 
     # Initialize the class for writing a file.
     def init_write(opts)
+      opts           = opts.dup
       @files_id      = opts.delete(:_id) || BSON::ObjectId.new
       @content_type  = opts.delete(:content_type) || (defined? MIME) && get_content_type || DEFAULT_CONTENT_TYPE
       @chunk_size    = opts.delete(:chunk_size) || DEFAULT_CHUNK_SIZE